Make XML parsing error message more explicit

[fengnanli]

There are two points in this pr:

1. when parsing the xml INodeSection, the state machine actually requires that must be the ending of a line, otherwise other states will kick in thus will result in errors.

2. expose the actual line under parsing in the exceptions for easier debugging, otherwise there is no clue what happened.

[xkrogen]

@fengnanli , can you look into the test failure? It looks legitimate.

[fengnanli]

@xkrogen so the parsing failed at this line: <directory><parent>16386</parent><inode>16390</inode></directory>
This line actually is not for the block report part <INodeSection> and it is in <INodeDirectorySection>. I will undo the change for the parser for </inode>, and file another pr to let the blockgen stop early when it finishes the INodeSection.

FYI, hdfs oiv 2.8.2 doesn't generate <inode> tag in the dir anymore, it is <child> instead.

[xkrogen]

Interesting... Thanks for the info! I would definitely welcome a change which supports the new-style <child> alongside the old-style <inode>. Annoying that it switched. I'll approve this change in the mean time.